/*
 * 3-D gear wheels.  This program is in the public domain.
 *
 * Command line options:
 *    -info      print GL implementation information
 *    -exit      automatically exit after 30 seconds
 *
 *
 * Brian Paul
 *
 *
 * Marcus Geelnard:
 *   - Conversion to GLFW
 *   - Time based rendering (frame rate independent)
 *   - Slightly modified camera that should work better for stereo viewing
 *
 *
 * Camilla Löwy:
 *   - Removed FPS counter (this is not a benchmark)
 *   - Added a few comments
 *   - Enabled vsync
 */

#if defined(_MSC_VER)
// Make MS math.h define M_PI
#define _USE_MATH_DEFINES
#endif

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define GLAD_GL_IMPLEMENTATION
#include <glad/gl.h>
#define GLFW_INCLUDE_NONE
#include <GLFW/glfw3.h>

/**

  Draw a gear wheel.  You'll probably want to call this function when
  building a display list since we do a lot of trig here.

  Input:  inner_radius - radius of hole at center
          outer_radius - radius at center of teeth
          width - width of gear teeth - number of teeth
          tooth_depth - depth of tooth

 **/

static void gear(GLfloat inner_radius, GLfloat outer_radius, GLfloat width, GLint teeth, GLfloat tooth_depth)
{
    GLint i;
    GLfloat r0, r1, r2;
    GLfloat angle, da;
    GLfloat u, v, len;

    r0 = inner_radius;
    r1 = outer_radius - tooth_depth / 2.f;
    r2 = outer_radius + tooth_depth / 2.f;

    da = 2.f * (float)M_PI / teeth / 4.f;

    glShadeModel(GL_FLAT);

    glNormal3f(0.f, 0.f, 1.f);

    /* draw front face */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i <= teeth; i++) {
        angle = i * 2.f * (float)M_PI / teeth;
        glVertex3f(r0 * (float)cos(angle), r0 * (float)sin(angle), width * 0.5f);
        glVertex3f(r1 * (float)cos(angle), r1 * (float)sin(angle), width * 0.5f);
        if (i < teeth) {
            glVertex3f(r0 * (float)cos(angle), r0 * (float)sin(angle), width * 0.5f);
            glVertex3f(r1 * (float)cos(angle + 3 * da), r1 * (float)sin(angle + 3 * da), width * 0.5f);
        }
    }
    glEnd();

    /* draw front sides of teeth */
    glBegin(GL_QUADS);
    da = 2.f * (float)M_PI / teeth / 4.f;
    for (i = 0; i < teeth; i++) {
        angle = i * 2.f * (float)M_PI / teeth;

        glVertex3f(r1 * (float)cos(angle), r1 * (float)sin(angle), width * 0.5f);
        glVertex3f(r2 * (float)cos(angle + da), r2 * (float)sin(angle + da), width * 0.5f);
        glVertex3f(r2 * (float)cos(angle + 2 * da), r2 * (float)sin(angle + 2 * da), width * 0.5f);
        glVertex3f(r1 * (float)cos(angle + 3 * da), r1 * (float)sin(angle + 3 * da), width * 0.5f);
    }
    glEnd();

    glNormal3f(0.0, 0.0, -1.0);

    /* draw back face */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i <= teeth; i++) {
        angle = i * 2.f * (float)M_PI / teeth;
        glVertex3f(r1 * (float)cos(angle), r1 * (float)sin(angle), -width * 0.5f);
        glVertex3f(r0 * (float)cos(angle), r0 * (float)sin(angle), -width * 0.5f);
        if (i < teeth) {
            glVertex3f(r1 * (float)cos(angle + 3 * da), r1 * (float)sin(angle + 3 * da), -width * 0.5f);
            glVertex3f(r0 * (float)cos(angle), r0 * (float)sin(angle), -width * 0.5f);
        }
    }
    glEnd();

    /* draw back sides of teeth */
    glBegin(GL_QUADS);
    da = 2.f * (float)M_PI / teeth / 4.f;
    for (i = 0; i < teeth; i++) {
        angle = i * 2.f * (float)M_PI / teeth;

        glVertex3f(r1 * (float)cos(angle + 3 * da), r1 * (float)sin(angle + 3 * da), -width * 0.5f);
        glVertex3f(r2 * (float)cos(angle + 2 * da), r2 * (float)sin(angle + 2 * da), -width * 0.5f);
        glVertex3f(r2 * (float)cos(angle + da), r2 * (float)sin(angle + da), -width * 0.5f);
        glVertex3f(r1 * (float)cos(angle), r1 * (float)sin(angle), -width * 0.5f);
    }
    glEnd();

    /* draw outward faces of teeth */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i < teeth; i++) {
        angle = i * 2.f * (float)M_PI / teeth;

        glVertex3f(r1 * (float)cos(angle), r1 * (float)sin(angle), width * 0.5f);
        glVertex3f(r1 * (float)cos(angle), r1 * (float)sin(angle), -width * 0.5f);
        u = r2 * (float)cos(angle + da) - r1 * (float)cos(angle);
        v = r2 * (float)sin(angle + da) - r1 * (float)sin(angle);
        len = (float)sqrt(u * u + v * v);
        u /= len;
        v /= len;
        glNormal3f(v, -u, 0.0);
        glVertex3f(r2 * (float)cos(angle + da), r2 * (float)sin(angle + da), width * 0.5f);
        glVertex3f(r2 * (float)cos(angle + da), r2 * (float)sin(angle + da), -width * 0.5f);
        glNormal3f((float)cos(angle), (float)sin(angle), 0.f);
        glVertex3f(r2 * (float)cos(angle + 2 * da), r2 * (float)sin(angle + 2 * da), width * 0.5f);
        glVertex3f(r2 * (float)cos(angle + 2 * da), r2 * (float)sin(angle + 2 * da), -width * 0.5f);
        u = r1 * (float)cos(angle + 3 * da) - r2 * (float)cos(angle + 2 * da);
        v = r1 * (float)sin(angle + 3 * da) - r2 * (float)sin(angle + 2 * da);
        glNormal3f(v, -u, 0.f);
        glVertex3f(r1 * (float)cos(angle + 3 * da), r1 * (float)sin(angle + 3 * da), width * 0.5f);
        glVertex3f(r1 * (float)cos(angle + 3 * da), r1 * (float)sin(angle + 3 * da), -width * 0.5f);
        glNormal3f((float)cos(angle), (float)sin(angle), 0.f);
    }

    glVertex3f(r1 * (float)cos(0), r1 * (float)sin(0), width * 0.5f);
    glVertex3f(r1 * (float)cos(0), r1 * (float)sin(0), -width * 0.5f);

    glEnd();

    glShadeModel(GL_SMOOTH);

    /* draw inside radius cylinder */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i <= teeth; i++) {
        angle = i * 2.f * (float)M_PI / teeth;
        glNormal3f(-(float)cos(angle), -(float)sin(angle), 0.f);
        glVertex3f(r0 * (float)cos(angle), r0 * (float)sin(angle), -width * 0.5f);
        glVertex3f(r0 * (float)cos(angle), r0 * (float)sin(angle), width * 0.5f);
    }
    glEnd();
}

static GLfloat view_rotx = 20.f, view_roty = 30.f, view_rotz = 0.f;
static GLint gear1, gear2, gear3;
static GLfloat angle = 0.f;

/* OpenGL draw function & timing */
static void draw(void)
{
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glPushMatrix();
    glRotatef(view_rotx, 1.0, 0.0, 0.0);
    glRotatef(view_roty, 0.0, 1.0, 0.0);
    glRotatef(view_rotz, 0.0, 0.0, 1.0);

    glPushMatrix();
    glTranslatef(-3.0, -2.0, 0.0);
    glRotatef(angle, 0.0, 0.0, 1.0);
    glCallList(gear1);
    glPopMatrix();

    glPushMatrix();
    glTranslatef(3.1f, -2.f, 0.f);
    glRotatef(-2.f * angle - 9.f, 0.f, 0.f, 1.f);
    glCallList(gear2);
    glPopMatrix();

    glPushMatrix();
    glTranslatef(-3.1f, 4.2f, 0.f);
    glRotatef(-2.f * angle - 25.f, 0.f, 0.f, 1.f);
    glCallList(gear3);
    glPopMatrix();

    glPopMatrix();
}

/* update animation parameters */
static void animate(void)
{
    angle = 100.f * (float)glfwGetTime();
}

/* change view angle, exit upon ESC */
void key(GLFWwindow *window, int k, int s, int action, int mods)
{
    if (action != GLFW_PRESS)
        return;

    switch (k) {
    case GLFW_KEY_Z:
        if (mods & GLFW_MOD_SHIFT)
            view_rotz -= 5.0;
        else
            view_rotz += 5.0;
        break;
    case GLFW_KEY_ESCAPE:
        glfwSetWindowShouldClose(window, GLFW_TRUE);
        break;
    case GLFW_KEY_UP:
        view_rotx += 5.0;
        break;
    case GLFW_KEY_DOWN:
        view_rotx -= 5.0;
        break;
    case GLFW_KEY_LEFT:
        view_roty += 5.0;
        break;
    case GLFW_KEY_RIGHT:
        view_roty -= 5.0;
        break;
    default:
        return;
    }
}

/* new window size */
void reshape(GLFWwindow *window, int width, int height)
{
    GLfloat h = (GLfloat)height / (GLfloat)width;
    GLfloat xmax, znear, zfar;

    znear = 5.0f;
    zfar = 30.0f;
    xmax = znear * 0.5f;

    glViewport(0, 0, (GLint)width, (GLint)height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-xmax, xmax, -xmax * h, xmax * h, znear, zfar);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -20.0);
}

/* program & OpenGL initialization */
static void init(void)
{
    static GLfloat pos[4] = {5.f, 5.f, 10.f, 0.f};
    static GLfloat red[4] = {0.8f, 0.1f, 0.f, 1.f};
    static GLfloat green[4] = {0.f, 0.8f, 0.2f, 1.f};
    static GLfloat blue[4] = {0.2f, 0.2f, 1.f, 1.f};

    glLightfv(GL_LIGHT0, GL_POSITION, pos);
    glEnable(GL_CULL_FACE);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);

    /* make the gears */
    gear1 = glGenLists(1);
    glNewList(gear1, GL_COMPILE);
    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, red);
    gear(1.f, 4.f, 1.f, 20, 0.7f);
    glEndList();

    gear2 = glGenLists(1);
    glNewList(gear2, GL_COMPILE);
    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, green);
    gear(0.5f, 2.f, 2.f, 10, 0.7f);
    glEndList();

    gear3 = glGenLists(1);
    glNewList(gear3, GL_COMPILE);
    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, blue);
    gear(1.3f, 2.f, 0.5f, 10, 0.7f);
    glEndList();

    glEnable(GL_NORMALIZE);
}

/* program entry */
int main(int argc, char *argv[])
{
    GLFWwindow *window;
    int width, height;

    if (!glfwInit()) {
        fprintf(stderr, "Failed to initialize GLFW\n");
        exit(EXIT_FAILURE);
    }

    glfwWindowHint(GLFW_DEPTH_BITS, 16);
    glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, GLFW_TRUE);

    window = glfwCreateWindow(300, 300, "Gears", NULL, NULL);
    if (!window) {
        fprintf(stderr, "Failed to open GLFW window\n");
        glfwTerminate();
        exit(EXIT_FAILURE);
    }

    // Set callback functions
    glfwSetFramebufferSizeCallback(window, reshape);
    glfwSetKeyCallback(window, key);

    glfwMakeContextCurrent(window);
    gladLoadGL(glfwGetProcAddress);
    glfwSwapInterval(1);

    glfwGetFramebufferSize(window, &width, &height);
    reshape(window, width, height);

    // Parse command-line options
    init();

    // Main loop
    while (!glfwWindowShouldClose(window)) {
        // Draw gears
        draw();

        // Update animation
        animate();

        // Swap buffers
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // Terminate GLFW
    glfwTerminate();

    // Exit program
    exit(EXIT_SUCCESS);
}
